EHCI: fix off-by-one error in ehci_submit_root()

USB devices on the 2nd port are not detected and I get the following message:

The request port(1) is not configured

That's with default CONFIG_SYS_USB_EHCI_MAX_ROOT_PORTS value of 2. 'req->index'
is 1-based, so the comparison in ehci_submit_root() can't be correct.

Signed-off-by: Sergei Shtylyov <sshtylyov@mvista.com>